Fluid power cylinder assemblies including, for example, hydraulic cylinder assemblies, are widely used to impart controlled motion to objects in many applications including, for example, construction, agricultural, industrial, aerospace, marine, and land vehicle applications. In some of these assemblies or applications, technical problems may include unintended drift or movement of the piston of the hydraulic cylinder assembly. Such drift may be caused by, for example, forces acting on the piston including weight of the piston and objects connected to it, seal or system leakage, cylinder housing internal surface damage, vibrations, or contamination. Additional technical problems may include alignment, assembly, complexity, cost, and reliability.
Various hydraulic locks may be used to lock and unlock hydraulic cylinders. One prior art fluid power cylinder assembly with a hydraulic lock is shown in U.S. Pat. No. 4,524,676, in which controlled hydraulic pressure in a bore 17 causes a plunger 17 to lift to permit extension or retraction of the piston of the assembly. Another fluid power cylinder assembly with a lock is shown in U.S. Pat. No. 5,097,748, in which a locking piston 11 holds balls 25 in a locked position to lock a piston 3 and releases the balls 25 in an unlocked position to allow the balls 25 to move out of groove 26 while executing a stroke. Another fluid power cylinder assembly with a lock is shown in U.S. Pat. No. 7,784,392, in which a bidirectional control relief valve 10 includes a poppet valve 30 that closes under certain conditions to seal off fluid volume 60 to lock a piston 12. Further, European Patent Application EP 1,197,668 A1 discloses a hydraulic lock device in which high pressure fluid from a pressure booster 7 acts on the outside of a thin wall sleeve 5 and deforms the sleeve 5 inwardly to lock a rod 3.
The present invention departs from these prior art hydraulic fluid power cylinder assemblies and addresses the above described and other technical problems and provides a fluid power cylinder assembly that is relatively easy to assemble and align and that has low complexity and low cost and high reliability.
At least one embodiment of the invention may provide a fluid power cylinder assembly that includes a cylinder body and a piston. The cylinder body may have a generally cylindrical interior surface defining a longitudinally extending cylinder chamber. The piston may have a generally cylindrical longitudinally extending piston body portion with a generally cylindrical exterior surface slidably disposed within the cylinder interior surface.
At least one embodiment of the invention may provide a drift stop body portion that may be fixed to the piston body portion and spaced laterally inwardly from the interior surface of the cylinder body. A longitudinally extending drift stop cavity may be defined by a longitudinally extending drift stop cavity wall, and the drift stop cavity may have an open end opening into the cylinder chamber. The drift stop cavity may be in open fluid pressure communication with the cylinder chamber under all conditions. The drift stop body portion may extend longitudinally into the drift stop cavity when the piston body portion and the drift stop body portion are each in one position. The drift stop body portion may be longitudinally spaced from the drift stop cavity when the piston body portion and the drift stop body portion are each in another position.
At least one embodiment of the invention may provide a drift stop blocking surface that may be carried by one of the drift stop cavity wall and drift stop body portion, and a laterally movable drift stop blocking member carried by the other of the drift stop cavity wall and the drift stop body portion. The drift stop blocking member may have one position engaging the drift stop blocking surface to limit longitudinal movement of the piston when the piston body portion and the drift stop body portion are each in their one position. The drift stop blocking member may have another position spaced from the drift stop blocking surface when the piston body portion and the drift stop body portion are each in their other position.
At least one embodiment of the invention may provide a drift stop blocking surface that may be carried by the drift stop cavity wall, and the drift stop blocking member may be carried by the drift stop body portion. The drift stop blocking member may be laterally aligned with and laterally spaced from the drift stop cavity wall when the drift stop body is received in the drift stop cavity. The drift stop body portion may extend longitudinally from the piston body portion. The combined lateral cross sectional area of the drift stop body portion within the drift stop cavity and piston body portion within the cylinder chamber may be substantially equal to the lateral cross sectional area of the cylinder chamber, and the combined lateral cross sectional area may be exposed to fluid pressure of the drift stop cavity and cylinder chamber under all conditions. The drift stop blocking member may be pressure balanced under all conditions. The force of fluid pressure acting on the combined lateral cross sectional area may provide the sole means for disengaging the drift stop blocking member from the drift stop blocking surface.
At least one embodiment of the invention may provide a laterally extending drift stop blocking member passage in the drift stop body portion, and the drift stop blocking member may be slidably disposed in the passage. An end cap may be fixed against movement relative to the cylinder body, and the drift stop cavity may be disposed in the end cap. A drift stop blocking member positioning surface may be provided, and the drift stop blocking member may engage the positioning surface to retain the drift stop blocking member away from the drift stop cavity wall and away from the cylinder interior surface when the drift stop blocking member and the drift stop surface are disengaged from one another. A drift stop blocking member spring may be carried by the drift stop body member, and the drift stop spring may bias the drift stop blocking member laterally outwardly against the positioning surface when the drift stop blocking member is disengaged from the drift stop blocking surface. The positioning surface may be a reduced diameter region of the passage.
At least one embodiment of the invention may provide the drift stop blocking surface including an annular ridge extending laterally inwardly from the drift stop cavity wall and at least one substantially conical surface. The drift stop blocking member may be generally spherical. The drift stop body portion may extend longitudinally from the piston body portion, and the piston body portion and the drift stop body portion may be of integral single piece construction. The piston body portion and the drift stop body portion may be concentrically disposed along a longitudinal axis.
This Summary is not intended to identify all key features or essential features of the claimed subject matter, and these and other features of the invention are more fully described and particularly pointed out in the description and claims set out below. The following description and claims and the annexed drawings set forth in detail certain illustrative embodiments of the invention, and these embodiments indicate but a few of the various ways in which the principles of the invention may be used.